1. Field of the Invention
The present invention relates to a solid-state image sensing device, and more particularly to a color linear image sensor.
2. Description of the Related Art
Conventionally, a solid-state image sensing device i.e. a CCD (Charge Coupled Device) linear image sensor has been used in a document reading apparatus such as a scanner, a facsimile machine, or a copying machine. In recent years, a color linear image sensor has also been widely used. There is known a solid-state image sensing device i.e. a color linear image sensor provided with pixel arrays of R, G, and B i.e. one-dimensional pixel arrays as disclosed in e.g. Japanese Unexamined Patent Publication No. 2002-142078 (D1). In use of the solid-state image sensing device in a document reading apparatus or a like apparatus, a scanning operation is performed by mechanically moving the solid-state image sensing device, or a focusing optical system, or a document in the document reading apparatus. In a normally operated condition, the one-dimensional pixel arrays are operative to successively read a document image at an identical position. If, however, a pitch of the one-dimensional pixel arrays is unduly large, an image at respective displaced positions may be read due to an operation error of the mechanical scanning operation. If the solid-state image sensing device is a color image sensor, an unduly large color displacement may occur in a reproduced image. In view of this, it is desirable to reduce the pitch of the one-dimensional pixel arrays.
In the conventional CCD linear image sensor, it is necessary to provide transfer gates and CCD shift registers between the one-dimensional pixel arrays in view of the construction of the image sensor. For instance, in the case where a solid-state image sensing device has three or more one-dimensional pixel arrays as disclosed in e.g. D1, the pitch of the one-dimensional pixel arrays is about four times as large as the pixel width i.e. the size of each pixel constituting the one-dimensional pixel arrays in a scanning direction. This may make it difficult to suppress the color displacement.
To solve the above drawback, e.g. Japanese Unexamined Patent Publication No. Hei 10-51602 (D2) or SONY CX-PAL (vol. 65), pp. 12-13 (D3) discloses a solid-state image sensing device, in which one-dimensional pixel arrays are arranged close to each other, in other words, the pitch of the one-dimensional pixel arrays is substantially identical to the pixel width of the one-dimensional pixel arrays in the scanning direction. It is, however, impossible to realize an arrangement that all the pixel array pitches of three or more one-dimensional pixel arrays are substantially identical to the pixel width in the solid-state image sensing device disclosed in D2. Also, it is required to reduce the pixel width i.e. the pixel size of at least one pixel array in a direction perpendicular to the scanning direction, in the solid-state image sensing device disclosed in D1. Consequently, this may make it difficult to design the solid-state image sensing device, or may lower the sensitivity in reading a document image.